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The Wells-Riley equation has been extensively used to quantify the infection risk of airborne transmission indoors. This equation is difficult to apply to actual conditions because it requires measurement of the outdoor air supply rate, which vary with time and are difficult to quantify. The method of determining the fraction of inhaled air that has been exhaled previously by someone in a building using a CO 2 concentration measurement can solve the limitations of the existing method. Using this method, the indoor CO 2 concentration threshold can be determined to keep the risk of infection below certain conditions. Based on the calculation of the rebreathed fraction, an appropriate mean indoor CO 2 concentration and required air exchange rate to control SARS-CoV-2 airborne transmission was calculated. The number of indoor occupants, ventilation rate, and the deposition and inactivation rates of the virus-laden aerosols were considered. The application of the proposed indoor CO 2 concentration-based infection rate control was investigated through case studies in school classrooms and restaurants. In a typical school classroom environment with 20–25 occupants and an exposure time of 6–8 h, the average indoor CO 2 concentration should be kept below 700 ppm to control the risk of airborne infection indoors. The ASHRAE recommended ventilation rate is sufficient when wearing a mask in classrooms. For a typical restaurant with 50–100 occupants and an exposure time of 2–3 h, the average indoor CO 2 concentration should be kept below about 900 ppm. Residence time in the restaurant had a significant effect on the acceptable CO 2 concentration. Given the conditions of the occupancy environment, it is possible to determine an indoor CO 2 concentration threshold, and keeping the CO 2 concentration lower than a certain threshold could help reduce the risk of COVID-19 infection. [ABSTRACT FROM AUTHOR]

To ensure smooth discharge of heat from air conditioning condensers in subway trains, it is important to keep the air temperature within the prescribed limit in the tunnel. Additionally, maintaining a suitable CO 2 concentration is essential for preserving air quality inside the carriages. In China, heat removal systems are commonly installed in subway tunnels to achieve these objectives, although the actual effectiveness has not been extensively examined. This paper focuses on a typical subway station in Tianjin. The effects of this system on tunnel temperature and CO 2 concentration were studied through field measurements and numerical simulations. The results indicate that the heat removal system introduces hot air from outside during summer leading to an increase in tunnel temperature, while the excluded air temperature is the average temperature in the tunnel. Since Tianjin is located in cold regions, the tunnel wall temperature decreases in winter, so the tunnel air can be cooled by tunnel walls in summer. The heat removal system has little impacts on the fresh air change rates, which are relatively 2.22 and 1.55 times per hour when the system is turned on or not. However, the maximum temperature and CO 2 concentration in the interval tunnel are 28.5 °C and 550 ppm, which are lower than the limitation of 40 °C and 1500 ppm even without the heat removal system. In conclusion, the installation of heat removal systems in subway tunnels located in cold regions is unnecessary. This can help reduce investments, save space, and minimize energy consumption. [ABSTRACT FROM AUTHOR]

Carbon can be transported into the deep mantle via subduction, thereby affecting the physical properties of the mantle, such as lowering the solidus, reducing the seismic velocity, and enhancing the electrical conductivity. However, constraining the quantity of recycled carbon in the mantle is challenging. Here, we present a method for quantitatively estimating the source CO 2 of Cenozoic nephelinites from eastern China. Experimental studies have shown that the CO 2 concentration of the basalt source is a function of the bulk partition coefficient of Ca between melt and its source. Based on the extremely high Ca contents of olivine phenocrysts from those nephelinites, our calculations indicate that those nephelinites from eastern China, which are thought to originate from a carbonated eclogite, were derived from a mantle source containing at least 0.2–5.2 wt% CO 2. This quantity is 1–2 orders of magnitude higher than the inferred CO 2 concentration in the MORB mantle. Our findings provide insights into estimating carbon concentration in the mantle and suggest that some parts of the mantle, most likely the mantle transition zone (MTZ), are extremely carbon-rich. This also offers an alternative explanation for the observed high electrical conductivity in the MTZ. • CO 2 content in the mantle is estimated by using olivine phenocryst compositions. • Source of Cenozoic nephelinites from eastern China contains at least 0.2–5.2 wt% CO 2. • Some parts of the mantle, most likely the mantle transition zone, are carbon-rich. [ABSTRACT FROM AUTHOR]

[Display omitted] • WUE increased significantly for main vegetation types in the Tibetan Plateau during 1982–2018; • Increased LAI boosted WUE in grassland while decreased VPD and elevated CO 2 derived WUE increase in broad-leaf forests; • Regression-based methods are too simplified and cannot fully reflect nonlinear effects of different drivers on WUE change. Ecosystem water use efficiency (WUE) is a key indicator for understanding the response of carbon–water processes to environmental changes. However, as affected by uncertainty of WUE estimation and attribution, the individual contributions of environmental drivers to WUE changes and the underlying mechanisms remain unclear on the Tibetan Plateau (TP). Here, a theory-based analytical WUE model was modified by introducing an optimal stomatal behavior model, and used to estimate monthly WUE and their drivers during 1982–2018 for main vegetation types on the Tibetan Plateau (TP). Rationality of three mainstream analytical attribution methods—analytical-based partial derivative method (APDM), regression-based partial derivative method (NPDM), and climate elasticity method (CEM)—was examined. Furtherly, the contributions of various environmental drivers to WUE variation trend were estimated for various vegetation types. Results indicate that: (1) The modified model performed well in estimating WUE against with observed WUE at five eddy-covariance (EC) flux stations, which decreased the uncertainty of WUE estimation. WUE increased significantly in the TP with a slope of 0.49 × 10-2 g C kg−1 H 2 O yr−1 during 1982–2018 with forests increased most rapidly; (2) Only APDM captured both the variation and magnitude of WUE trends, and both NPDM and CEM failed to reproduce the magnitude of WUE trends, though CEM was better than NPDM benefited from its nonlinear structure. Through comparing these methods, we found that the nonlinear direct effects of these forcing variables on WUE change could be higher than their indirect effects caused by their interactions. (3) There are some differences in the main drivers of WUE trends for various vegetation types. Increase in WUE was mainly driven by the increase in leaf area index (LAI) for both steppes and meadows, while decreased air water vapor pressure deficit (VPD) and elevated CO 2 showed higher positive effects for broad-leaf forests. The distinct response and extremely scarce EC observations of forests suggest that more attention should be paid to forests in the TP. This study could help in selection of attribution methods and understanding the mechanisms of carbon–water coupling of alpine ecosystems under a changing climate. [ABSTRACT FROM AUTHOR]

[Display omitted] • The yield of hexanoic acid increased by 58% with the addition MgCO 3. • Mg2+ and NH 4 + mitigated the excessive ethanol oxidation, while Ca2+ facilitated it. • Batch addition of NaHCO 3 enhanced the synthesis of hexanoic acid. • High CO 2 concentration facilitated the proliferation of Uribacillus and Prevotella. • Clostridium_sensus_stricto_ 12 was the main hexanoic acid-producing bacterium. Carbon dioxide (CO 2) plays a crucial role in carbon chain elongation with ethanol serving as an electron donor. In this study, the impacts of various carbonates on CO 2 concentration, hexanoic acid production, and microbial communities during ethanol-butyric acid fermentation were explored. The results showed that the addition of MgCO 3 provided sustained inorganic carbon and facilitated interspecific electron transfer, thereby increasing hexanoic acid yield by 58%. MgCO 3 and NH 4 HCO 3 inhibited the excessive ethanol oxidation and decreased the yield of acetic acid by 51% and 42%, respectively. The yields of hexanoic acid and acetic acid in the CaCO 3 group increased by 19% and 15%, respectively. The NaHCO 3 group exhibited high headspace CO 2 concentration, promoting acetogenic bacteria enrichment while reducing the abundance of Clostridium_sensu_stricto_ 12. The batch addition of NaHCO 3 accelerated the synthesis of hexanoic acid and increased its production by 26%. The relative abundance of Clostridium_sensus_stricto_ 12 was positively correlated with hexanoic acid production. [ABSTRACT FROM AUTHOR]

• We report on air quality intervention in 60 student dwellings in Denmark and Switzerland. • Visual air quality feedback significantly altered user behavior in half of the dwellings. • Air quality awareness led to reduced median CO 2 levels in 77% of bedrooms. • Air quality awareness doubled the ventilation rates in 70% of dwellings. • Display-integrated CO 2 monitoring is an effective air quality intervention in student dwellings. Although existing standards typically prescribe fixed ventilation rates, a large portion of the building stock lacks mechanical ventilation systems. Such buildings obtain outdoor air through unintentional infiltration, open windows, and the operation of exhaust fans, which are mainly dependent on user awareness and behavior. This study investigates whether the presence of a simple CO 2 meter display can alter user behavior and improve indoor air quality (IAQ) in dwellings. We conducted a two-week monitoring of CO 2 concentration, air temperature, and relative humidity in 60 student dwellings (bedrooms and living rooms) in Denmark and Switzerland. During the first week, the CO 2 display was concealed, and occupants adhered to their usual routines. In the second week, occupants used the display's visual feedback to enhance IAQ when necessary. Results revealed that over 95% of dwellings witnessed a reduction in median CO 2 levels during the second week, both overall and in individual rooms. Furthermore, a descriptive analysis of CO 2 concentration step changes exceeding the thresholds of "normal variation" showed an increase in the number of negative step changes, indicating a shift in user behavior. These findings underscore the efficacy ofa display interface providing information on the indoor environment in triggering behavior changes and improving IAQ in dwellings. [ABSTRACT FROM AUTHOR]

Summer monsoon rainfall in East Asia gradually strengthens in response to CO 2 increase (ramp-up period), but this reverses slowly following CO 2 decrease (ramp-down period), showing an asymmetric behavior in a changing CO2 pathway. [Display omitted] Understanding the regional hydrological response to varying CO 2 concentration is critical for cost-benefit analysis of mitigation and adaptation polices in the near future. To characterize summer monsoon rainfall change in East Asia in a changing CO 2 pathway, we used the Community Earth System Model (CESM) with 28 ensemble members in which the CO 2 concentration increases at a rate of 1% per year until its quadrupling peak, i.e., 1468 ppm (ramp-up period), followed by a decrease of 1% per year until the present-day climate conditions, i.e., 367 ppm (ramp-down period). Although the CO 2 concentration change is symmetric in time, the amount of summer rainfall anomaly in East Asia is increased 42% during a ramp-down period than that during a ramp-up period when the two periods of the same CO 2 concentration are compared. This asymmetrical rainfall response is mainly due to an enhanced El Niño-like warming pattern as well as its associated increase in the sea surface temperature in the western North Pacific during a ramp-down period. These sea surface temperature patterns enhance the atmospheric teleconnections and the local meridional circulations around East Asia, resulting in more rainfall over East Asia during a ramp-down period. This result implies that the removal of CO 2 does not guarantee the return of regional rainfall to the previous climate state with the same CO 2 concentration. [ABSTRACT FROM AUTHOR]

How hydrothermal factors and CO 2 concentration affect the vegetation carbon sink over time and across elevation gradients is crucial for carbon sequestration and enhancement, which remains unclear. Here, the temporal changes of the interannual relationship of net primary productivity (NPP) with hydrothermal factors and CO 2 concentration over elevation were revealed using ensemble empirical mode decomposition (EEMD) method and moving window-based multiple regression analysis during 1981–2018, in a case study of six provinces along the 'Maritime Silk Road' of China. We found that: (1) except for low-elevation farmland, the interannual relationship of vegetation NPP with CO 2 (R NPP-CO2), precipitation accumulation (R NPP-PA), soil moisture (R NPP-SM), downward surface shortwave radiation (R NPP-SR) and minimum temperature (R NPP-TMN) is mainly positive, while the relationship with maximum temperature (TMAX, R NPP-TMX) and vapor pressure deficit (VPD, R NPP-VPD) is mainly negative, indicating that most hydrothermal factors can increase NPP except TMAX and VPD. Most of the interannual relationship is strengthening, especially for thermal factor, indicating the strengthened impacts of hydrothermal factors and CO 2, while the weakening relationship with hydrological factors accounted for large areas, which cannot be ignored. (2) With increasing elevation, the positive R NPP-CO2 diminished, while the positive R NPP-SM and the negative R NPP-VPD amplified, indicating the positive impacts from CO 2 decreased, while those from SM and VPD increased. Meanwhile, R NPP-SR , R NPP-TMN , and R NPP-PA reversed from positive to negative, while R NPP-TMX reversals from negative to positive, indicating reversed impacts. (3) With increasing elevation, the temporal changes of positive R NPP-CO2 and R NPP-SM varied from weakening to strengthening and from strengthening to weakening, respectively, while those of R NPP-SR and R NPP-TMN together with R NPP-PA varied from strengthening positive to strengthening negative and weakening negative, respectively. Meanwhile, the strengthening negative of R NPP-TMX , and R NPP-VPD , changed to weakening positive and weakening negative, respectively. Our study highlights the importance of the divergent trends of the interannual relationship of NPP with hydrothermal factors and CO 2 concentration across elevation for accurate prediction of future carbon sink potential under global change. [Display omitted] • Interannual relationships between environmental factors and NPP were mostly positive. • Interannual relationship are strengthening, especially for thermal factors. • Elevation has significant effects on the temporal trends below 200m and above 1000m. • The relationship showed divergent trends across elevation. [ABSTRACT FROM AUTHOR]

• A Transformer-based data-driven model is developed to predict CO 2 concentration and FG flowrate for a waste fired CHP plant. • The impact of different meteorological parameters is investigated as input features. • The Transformer model can give better accuracy than LSTM and ANN. • Including NIR spectral data can improve the accuracy of the Transformer model. Integrating CO 2 capture with biomass-fired combined heat and power (bio-CHP) plants is a promising method to achieve negative emissions. However, the use of versatile biomass, including waste, and the dynamic operation of bio-CHP plants leads to large fluctuations in the flowrate and CO 2 concentration of the flue gas (FG), which further affect the operation of post-combustion CO 2 capture. To optimize the dynamic operation of CO 2 capture, a reliable model to predict the FG flowrate and CO 2 concentration in real time is essential. In this paper, a data-driven model based on the Transformer architecture is developed. The model validation shows that the root mean squared error (RMSE), mean absolute percentage error (MAPE), and Pearson correlation coefficient (PPMCC) of Transformer are 0.3553, 0.0189, and 0.8099 respectively for the prediction of FG flowrate; and 13.137, 0.0318, and 0.8336 respectively for the prediction of CO 2 concentration. The potential impact of various meteorological parameters on model accuracy is also assessed by analyzing the Shapley value. It is found that temperature and direct horizontal irradiance (DHI) are the most important factors, which should be selected as input features. In addition, using the near-infrared (NIR) spectral data as input features is also found to be an effective way to improve the prediction accuracy. It can reduce RMSE and MAPE for CO 2 concentration from 0.2982 to 0.2887 and 0.0158 to 0.0157 respectively, and RMSE and MAPE for FG flowrate from 4.9854 to 4.7537 and 0.0141 to 0.0121 respectively. The Transformer model is also compared to other models, including long short-term memory network (LSTM) and artificial neural network (ANN), which results show that the Transformer model is superior in predicting complex dynamic patterns and nonlinear relationships. [ABSTRACT FROM AUTHOR]

Previous research in CO 2 electroreduction primarily focused on cathodic electrocatalysts and electrode configurations using pure CO 2. Few studies explored the impact of residence time and N 2 /O 2 compounds, crucial for practical industrial implementation. In this study, the effect of residence time and the influence of N 2 and O 2 compounds on CO 2 electroreduction to formate are investigated, employing Bi carbon-supported nanoparticles in the form of Gas Diffusion Electrodes within an electrochemical flow reactor with a single pass of the reactants. The results highlight the critical role of residence time and the impact of N 2 and O 2 compounds in the CO 2 electroconversion process. On the one hand, the evaluation of residence time holds paramount significance for the potential establishment of a large-scale CO 2 recycling plant, as it has the potential to significantly impact both the capital and operational costs of the integrated electrolyzer-separator system. Optimal results are obtained in the range of residence times between 1.8 and 2.9 seconds, corresponding to CO 2 flow rates of 150 and 250 mL·min−1, respectively. On the other hand, the study resulted in a promising Faradaic Efficiency for formate of 75.0%, with similar values achieved at CO 2 concentrations in the range of 75 – 100 vol%. These results are particularly noteworthy as they demonstrate that achieving a CO 2 capture efficiency of 100% is not necessary, thereby reducing the costs associated with this process and, consequently, the overall cost of integrating both capture and utilization processes in a CO 2 recycling plant. [Display omitted] • Residence time impacts CO2 electroreduction to formate on Bi cathodes. • N2 and O2 compounds' influence on CO2 to formate electroreduction. • Consistent results with CO2 concentrations ≥75 vol%. • Optimal outcomes in residence time: 1.8–2.9 seconds. • Integrating capture and utilization lowers overall cost. [ABSTRACT FROM AUTHOR]

• Potential use of fluidized bed bioreactor to grow microalgae on polyurethane foam. • Optimum light intensity and CO 2 interaction to spur attached microalgal growth. • N-rich real wastewater impact on mechanism of microalgal attachment formations. • Consequential reusability of fluidized bed on microalgae-based biodiesel quality. Impoverishing nutrients from wastewater via assimilation into microalgal biomass has gained footprint in bioremediation technologies. To ease the harvesting of mature microalgal biomass from effluent, this study proposed the employment of fluidized bed bioreactor to grow attached microalgal biomass onto polyurethane foam support material while bioremediating the N-rich real wastewater from chemical fertilizer manufacturing industry. The complete removals of all nitrogen species (NH 4 +-N, NO 2 −-N and NO 3 −-N) together with COD and total phosphorus were achieved at the optimum light intensity and CO 2 concentration of 216 μmol/m2 s and 9.1 %, respectively, giving rise to the attached microalgal biomass productivity of 0.094 g/L/day. These performances were also found maintaining for at least 4 cycles of reiterative uses of spent polyurethane foam support material in similar fluidized bed bioreactor setup condition with every cycle being introduced with fresh N-rich real wastewater. The mechanism of attachment formations study predicted that the polysaccharides and proteins from microalgal extracellular polymeric substances had bridged the cells onto polyurethane foam support material during the initial colonization prior to populating and growing to cover the surfaces of support material. For biodiesel production, the extracted neutral lipid content of attached microalgal biomass was found to be four times higher than the suspended growth culture. From the transesterification process, about 97 %–98 % of attached microalgal lipid could be converted into fatty acid methyl esters (FAMEs) mixture. Interestingly, the degree of saturated fatty acids (SFA) in FAMEs was recorded increasing with the increase of cycles of reusing spent polyurethane foam support material. The presence of more SFA in FAMEs could overall enhance the oxidative stability and contribute to higher cetane number of produced biodiesel from facilely harvested attached microalgal biomass. [ABSTRACT FROM AUTHOR]

• The optimal control of environmental conditions is an effective way for improving plant growth, quality, and input resources use efficiency. • Light is the main source of energy required for photosynthesis and many other physiological processes related to plant growth. • Light quality influences plant growth and development more than light intensity and photoperiod. • Light spectrum for plant response ranges from the UV (280–400 nm) to the far-red (700–800 nm) regions. • More studies are still needed, taking into account integrative environmental control, input resources efficiency, and economic analysis. Lettuce is one of the most popular leafy vegetables produced in controlled environments with artificial lighting (CEALs). Optimal control of environmental conditions can be used to facilitate the improvement of lettuce plant growth and light use efficiency. This article reviews and discusses the effects of light, air velocity, temperature, relative air humidity, and CO 2 concentration on the growth and development of lettuce plants in a CEAL. A review of previous studies revealed that light intensity in the range between 200–250 µmol m−2 s−1 with a photoperiod of 16–18 h using red and blue LEDs, with a ratio between 5 and20% for the blue light are optimal to improve lettuce plant growth and light use efficiency. The optimal light quality can also be achieved by using supplemental white or green LEDs, far-red light, and UV-A radiation. Air velocity in the range between 0.3 and 0.7 m s−1 enhances the photosynthetic rate, transpiration rate, and gas diffusion through the boundary layer of the leaf and prevents the occurrence of tipburn. The air temperature of 22–25 °C during the light periods was reported as optimal to enhance CO 2 uptake and consequently improve lettuce growth. Relative air humidity in the range between 70 and 80% promotes vegetative growth and reduces water stress by causing the stomata to close. High CO 2 concentrations increased photosynthetic rate but also decreased CO 2 utilization efficiency. Therefore, CO 2 concentration in the range between 1000 and 1500 µmol mol−1 is optimal for high growth rate, productivity, and CO 2 utilization efficiency. Most of the previous studies have focused on the effect of light intensity, quality, and duration on the growth and development of lettuce plants under artificial light, with limited information about the interactions of all environmental conditions. This review will be useful for growers, researchers, and designers in the field of plant production in CEALs. [ABSTRACT FROM AUTHOR]

• The microstructural and mechanical performances of dry-mix cement paste in view of CO 2 concentration and further water curing was investigated in detail. • The compressive strength and microstructure at 2 h (immediately after carbonation) and 1, 3 and 7 days with further water curing was explored. • The hydrated and carbonated products was analyzed by XRD and TGA. The microstructure change of C-S-H and calcium carbonate was further analyzed by NMR and SEM. Early-age carbonation can make a significant difference in the formation of hydration products in cement-based materials and alter the microstructural and mechanical performances. To understand in detail the impacts and their contribution to cement hydration, dry-mix cement pastes were exposed to instant carbonation with 0.04 %, 1%, 3%, 10 %, 20 % CO 2 concentrations for 2 h prior to further water curing. By increasing the CO 2 concentration, an increment in strength gain of samples at 2 h (right after early carbonation) as well as being prolonged by water curing at 1, 3, 7 days was noticed. This agrees with TGA and XRD results, demonstrating that the increases in CO 2 concentration resulted in a higher carbonation reaction and hydration degree. 29Si NMR results also indicate that the higher the CO 2 concentration the lower the calcium to silica ratio (Ca/Si); thus, there is a higher degree of polymerization to promote early hydration. It can be concluded that early carbonation of 2 h in particular with a high CO 2 concentration can be beneficial for further cement hydration due to the consumption of calcium hydroxide (CH) and nuclei site effect of calcite crystals, resulting in better microstructural properties and mechanical performance. [ABSTRACT FROM AUTHOR]

• A study combined experiment and numerical analysis was firstly performed to improve the ventilation system in a Mine refuge chamber (MRC). • A new analytical model of fifty-person MRC is proposed. • Average CO 2 concentration can be controlled below 0.5 % by ventilation of 0.1 m3/min per person. • Air inlets arranged on both sides or top and air outflows arranged on both ends of the MRC are recommended. • A quantitative relationship between CO 2 concentration and ventilation rate, CO 2 release rate was proposed. A combined experimental and numerical study was performed to improve the performance of the ventilation system in a mine refuge chamber (MRC). In the experiment, CO 2 cylinders and dispersion pipes were used to simulate the CO 2 release of 50 people, and 0.1 L/min per person of fresh air was provided by an air compressor. A new analytical model for a 50-person MRC was proposed and validated against the experimental data. Sensitivity analysis was carried out to investigate the effects of several control factors. The results indicated the following: (1) The ventilation system layout has a significant influence on the CO 2 concentration distribution in an MRC, while the uniformity of the CO 2 concentration distribution in the MRC may not be effective with increased number of air inlets. (2) Under a well-arranged ventilation system in the 50-person MRC, the average CO 2 concentration can be controlled at less than 0.5 % with a ventilation rate of 0.1 m3/min per person, and less than 0.2 % with a ventilation rate of 0.3 m3/min per person. (3) A quantitative correlation exists between the CO 2 concentration and ventilation volume rate, as well as the CO 2 release rate, for an MRC under a well-arranged ventilation system. [ABSTRACT FROM AUTHOR]

CO 2 -based demand-controlled ventilation (DCV) requires placement of CO 2 sensors in air handling units (AHUs) as well as in individual zones. In complex multi-zone systems or across building portfolios, the installation and maintenance costs of these sensors are non-negligible. This study explores how CO 2 sensor grids can be configured in a sparser manner to allow for CO 2 -based DCV of spaces adjacent to zones with CO 2 sensors that may not have sensing infrastructure themselves. A simulation-based study of a 26-zone office building was conducted under a variety of occupancy schedules, number and placement of zone-level CO 2 sensors, and with and without motion detectors to determine how RP-1747 DCV impacted heating, ventilation, and air conditioning (HVAC) energy use and zone CO 2 concentrations when implemented traditionally or with adjacent control, for a total of 29,730 simulations. It was found that CO 2 sensors installed in approximately 31% of zones could effectively enable CO 2 -based DCV across the entire floor plate with a negligible impact on the number of hours where CO 2 concentrations were elevated, resulting in 7.3% to 17.4% higher HVAC energy savings compared to individual control of spaces in the case study building. [ABSTRACT FROM AUTHOR]

This study presents that increases in atmospheric CO 2 levels impact the ventilation and energy in buildings. The most significant impact of ventilation occurs during use, because of the indoor air quality. According to the 2014 IPCC report, observed atmospheric CO 2 levels increased at a rate of 1.9–2.1 ppm per year. This study measured CO 2 levels in a building in an urban area in Shanghai, China, and analyzed existing ventilation performance and energy simulation in relation to the impact of increased atmospheric CO 2 concentrations. As long as the atmospheric CO 2 level increased, the outdoor airflow rate had to increase also to maintain an acceptable indoor CO 2 level. The ventilation rate was also considered in relation to the surrounding environment. In Shanghai, the average value of CO 2 concentrations on an auto road was 550 ± 20 ppm and the average value on a pedestrian road was 435 ± 15 ppm. A building that was surrounded by high traffic roads needed 20–30% more outdoor airflow rate than a building surrounded by pedestrian roads. Accordingly, energy loads in buildings, for heating and cooling were also affected. In order to dilute indoor CO2 level, the thermal ventilation energy and the ventilation energy uniformly provided a 20% energy load increase during the 12 months, while each monthly energy load varied, depending on the season and/or month. By analyzing indoor CO 2 levels and the rise in atmospheric CO 2 levels, this study determined how these rises impacted the energy consumption of the building, and how to design a new outdoor airflow supply rate to adapt to a changed environmental condition. • How a rise in atmospheric CO 2 concentrations impacts energy consumption in a building. • How to design new outdoor airflow supply rates to adapt to ambient conditions. • Indoor air ventilation performance governed by urban factors and climate changes. • Outdoor air supply rate must be increased by 10% per 50 ppm of the CO2 level rise. [ABSTRACT FROM AUTHOR]

• Experimental testing of recycled aggregate concrete carbonation resistance. • Experimental testing of high volume fly ash concrete carbonation resistance. • Analysis of CO 2 concentration level on carbonation process. • Prediction of carbonation depth based on accelerated tests and exposure time. • Evaluation of fib carbonation model on different concrete types. The reuse of industrial residue streams such as fly ash (FA) or waste materials such as recycled concrete aggregate (RCA) can be beneficial both from an economic and an ecological point of view. Extensive research, investigating different properties of these concrete types, has been carried out so far. However, durability remains a key property ensuring sustainable application of these materials in the construction sector that still needs more research to be fully understood. The main objective of this study was to evaluate the application of widely used models for carbonation depth prediction—defined for ordinary Portland cement concrete with natural aggregate (NAC)—to high volume FA concrete (HVFAC) and recycled aggregate concrete (RAC). The research presented in this paper was conducted in two steps. First, an experimental programme was designed to provide better understanding of the influence of different CO 2 concentrations on the carbonation process kinetics in HVFAC, RAC and NAC. This was performed using accelerated carbonation tests (CO 2 concentrations of 1%, 2%, 4% and 16%) and natural carbonation tests (duration 21 and 48 months). Furthermore, a database of previously published results of HVFAC and NAC carbonation depths was made in order to analyse the application of carbonation depth prediction defined by Tuutti and given in the fib Model Code 2010. It was shown that the existing models, providing the relationship between accelerated test results and natural carbonation depth, are applicable to NAC and RAC but not to HVFAC. Modifications of the above mentioned models were proposed in order to enable a more accurate and reliable prediction of the HVFAC carbonation depth under natural exposure conditions. [ABSTRACT FROM AUTHOR]

• We explore the effect of heavy metals on CO 2 assimilation and stomatal conductance in a common urban tree in Mexico City. • PAR had the greatest effect on A ; whereas T A and VPD had the greatest effect on g S • There were not differences in the foliar internal concentrations of heavy metals between the studied sites. • We found a lower stomatal density at the site with the highest concentration of pollutants. • This finding represents a possible mechanism to avoid internal damage by these. Urban trees reduce CO 2 and pollutants that represent a risk for human health in cities. In this work, we assessed the potential effect of heavy metals and environmental variables on the CO 2 assimilation (A) and the stomatal conductace (g S) of Ligustrum lucidum , a common urban tree in Mexico City. We compared two sites with contrasting pollution levels: 1) city centre (PPI-C, high pollution level); and 2) south of the city (CU-SW; low pollution level). At each site, we measured 1) phsysiological traits (A and g S); 2) environmental variables (photosynthetically active radiation, PAR; air temperature, T A ; vapor pressure deficit, VPD ; concentration of atmospheric CO 2); and 3) morphological leaf characteristics (stomatal size and density). Concentration of the heavy metals Pb, Cd, Cr, Cu, Mn, Fe, and Zn was determined in washed (internal metals) and unwashed (external plus internal metal) leaves at both sites. CO 2 assimilation at CU-SW was higher than at PPI-C. PAR had the greatest effect on A ; whereas T A and VPD had the greatest effect on g S. Regarding heavy metals, although we found no significant differences in internal concentrations between sites, we found a lower stomatal density at PPI-C, which may indicate a response of the species to the local pollution conditions. This characteristic might be benefitial for the species, allowing it to maintain optimal physiological conditions by reducing the assimilation of pollutants. Our results suggest that L. lucidum is a well adapted species for the urban environment. [ABSTRACT FROM AUTHOR]

Abstract Microalga is a promising candidate for bio-mitigation of CO 2. It has been longtime recognized that high CO 2 concentration would impose stresses on microalga to suppress the growth. However, this concept was challenged in this research by investigating the growth, photosynthesis and anti-oxidant characteristics of Arthrospira platensis under independent effects of CO 2 concentrations and pH. Results showed the growth of A. platensis was only inhibited when broth was in acidic pH. Microalgal cells could deal with high CO 2 concentration readily if medium pH was maintained in favorite level. Photosynthesis was inhibited swiftly and significantly under acidified condition. The singlet oxygen was produced in low level for alkalic pH treatment, however it burst quickly after low pH stress was imposed. Accordingly, it was proposed that the phenomena of high CO 2 intolerance was caused by CO 2 induced pH decline rather than high CO 2 concentration itself. This finding has significance on large scale application of microalga based CO 2 mitigation and flue gas treatment since it proved concentrated CO 2 could be directly assimilated without dilution. Graphical abstract Unlabelled Image Highlights • The 'CO 2 intolerance' for microalgae might be a pseudo-proposition. • Growth inhibition of microalga was caused by CO 2 induced acidification. • This finding has significance on microalga based CO 2 bio-mitigation. [ABSTRACT FROM AUTHOR]

Abstract The elevation of atmospheric CO 2 is an inevitable trend that would lead to significant impact on the interrelated carbon and nitrogen cycles through microbial activities in the aquatic ecosystem. Eutrophication has become a common trophic state of inland waters throughout the world, but how the elevated CO 2 affects N cycles in such eutrophic water with algal bloom, and how vegetative restoration helps to mitigate N 2 O emission remains unknown. We conducted the experiments to investigate the effects of ambient and elevated atmospheric CO 2 (a[CO 2 ], e[CO 2 ]; 400, 800 μmol﹒mol−1) with and without the floating aquatic plant, Eichhornia crassipes (Mart.) Solms, on N-transformation in eutrophic water using the 15N tracer method. The nitrification could be slightly inhibited by e[CO 2 ], due mainly to the competition for dissolved inorganic carbon between algae and nitrifiers. The e[CO 2 ] promoted denitrification and N 2 O emissions from eutrophic water without growth of plants, leading to aggravation of greenhouse effect and forming a vicious cycle. However, growth of the aquatic plant, Eichhornia crassipes , slightly promoted nitrification, but reduced N 2 O emissions from eutrophic water under e[CO 2 ] conditions, thereby attenuating the negative effect of e[CO 2 ] on N 2 O emissions. In the experiment, the N transformation was influenced by many factors such as pH, DO and algae density, except e[CO 2 ] and plant presence. The pH could be regulated through diurnal photosynthesis and respiration of algae and mitigated the acidification of water caused by e[CO 2 ], leading to an appropriate pH range for both nitrifying and denitrifying microbes. Algal respiration at night could consume DO and enhance abundance of denitrifying functional genes (nirK , nosZ) in water, which was also supposed to be a critical factor affecting denitrification and N 2 O emissions. This study clarifies how the greenhouse effect caused by e[CO 2 ] mediates N biogeochemical cycle in the aquatic ecosystem, and how vegetative restoration mitigates greenhouse gas emission. Graphical abstract Unlabelled Image Highlights • Elevated atmospheric CO 2 (e[CO 2 ]) promotes denitrification and N 2 O emissions from eutrophic water without plant. • Algal activity is the main driving factor leading to inhibited nitrification but enhanced N 2 O emissions under e[CO 2 ]. • Floating aquatic plant cultivation attenuate the negative effect on enhanced N 2 O emissions caused by e[CO 2 ] [ABSTRACT FROM AUTHOR]

• The stomatal conductance (g s) decreased at a diminishing rate as the CO 2 increased. • The modified hyperbolic model (MH) provided the best estimate of g s. • The MH gave the best ET estimate when applied into P-M model under increased CO 2. • Changes of the empirical parameter b in MH had a minimal effect on predicted ET. An increase in atmospheric CO 2 concentration (CO 2) affects stomatal conductance (g s). Since g s is an important parameter in the Penman–Monteith model (P-M), an accurate estimate of g s can improve the accuracy of the estimation of evapotranspiration (ET) by P-M when CO 2 increases. This paper identifies three models of the relationship between g s and CO 2 (the linear model , L, the hyperbolic model , H, and the modified hyperbolic model , MH), and compares their estimations of ET when they are incorporated into P-M. A two-year experiment which included four levels (400, 550, 700, and 900 μmol mol−1) and three levels (400, 550, and 700 μmol mol−1) of CO 2 in 2015 and 2016, respectively, was conducted in order to obtain validation data. Fifty papers that had studied the effect of increased CO 2 on g s , over a 45-year period, were analyzed to obtain calibration data. After being calibrated and validated, each of the three models was in turn included as a component of P-M to estimate ET under increased CO 2 , followed by the comparison between estimated and observed ET. The sensitivity of P-M to the parameters in three models was also analyzed. Our results show that g s decreased and the reduction rate gradually lessened as CO 2 increased. Of the three models, MH gave the best estimate of g s , having the largest values of the coefficient of determination (R 2), 0.97, the Nash–Sutcliffe efficiency coefficient (NSE), 0.96, and the modified affinity index (d), 0.93, and the smallest values of the root mean square error (RMSE) , 0.03, and the Akaike information criterion (AIC) , −47.48. Each of the three models gave different ET results for different levels of CO 2 when used as a component of P-M. The MH had better ET estimations than L and H when compared to observed ET across all CO 2 concentration levels, with the highest R2 , NSE , and d , and the lowest RMSE and AIC. The sensitivity of P-M to the empirical parameters varied among the three models, for instance, ±40 and ±20% changes of parameter p in L, g s max p and C s 0 in H, and b in MH resulted in −15 to 4%, −13 to 7%, −9 to 4%, and −3 to 3% changes in predicted ET , respectively. Thus, changes of parameter b in MH had minimum effect on predicted ET , indicating greater stability of P-M in ET estimation by incorporating MH. Therefore, using MH to model the response of g s to increased CO 2 when incorporated into P-M to estimate ET not only represents a more appropriate stomata physiological reaction to higher CO 2 , but also results in a more accurate estimate of ET , and making the model more broadly applicable. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Modeling of attached microalgal growth onto fluidized polyurethane foam support. • Optimum interactive light intensity and dissolved CO 2 to grow attached microalgae. • Bioremediation of nutrients-rich wastewater to grow attached microalgae. • Biofixation of CO 2 into attached microalgae-based lipid for biodiesel production. Abstract One way to reconcile an issue associating with the harvesting of microalgal biomass is via the application of attached growth cultivation mode, whereby the mature microalgal biomass can be facilely harvested from the support material. Accordingly, the objectives of present works were to model the attached growth of Chlorella vulgaris onto polyurethane foam support material in a fluidized bed bioreactor while simultaneously bioremediating real nutrients-rich wastewater and biofixing CO 2 for biodiesel production. The mathematical models accounting the impact of various interactions between light intensities and CO 2 concentrations in culture medium on growing attached microalgal biomass were initially improved. The successful practicality of models was confirmed from the analysis of statistical accuracy while predicting the growth of attached microalgal biomass in real nutrients-rich wastewater. When the microalgal growth reached the stationary growth phase, all the nutrients (nitrogen and phosphorous sources of compounds) were completed impoverished, accentuating the bioremediation potentiality in satisfying the effluent discharged requirements. Subsequently, the modeling of microalgal CO 2 biofixation also unveiled that the highest CO 2 biofixation rate was transpiring in parallel with the growth rate of attached microalgal biomass during the exponential growth phase. Upon the harvesting, the neutral lipid from mature attached microalgal biomass was found to contain 97.7% (by wt. of lipid) of fatty acid methyl esters (FAMEs) mixture, heralding the biodiesel purity. Assessment of biodiesel quality showed a balance composition among the saturated, monounsaturated and polyunsaturated FAMEs mixture with high in C16 and C18 FAME species for the materialization of efficient combustion. [ABSTRACT FROM AUTHOR]

Highlights • In-situ and real-time measurement of dissolved CO 2 during CO 2 hydrate formation. • Drastic drop of dissolved CO 2 was observed during CO 2 hydrate crystallization. • CO 2 gas diffusion to the liquid was identified as the rate-limiting step. • Local equilibrium between liquid and solid phases was identified. Abstract Gas hydrates are regarded as promising materials for various potential applications. In particular, CO 2 hydrates are known for their cold storage capacities, related to their high latent heat of melting. They could be used as high efficiency Phase Change Materials in Phase Change Slurries for secondary refrigeration loops. A better understanding of the crystallization mechanism of CO 2 hydrates in slurries and of the resulting formation kinetics is still needed to evaluate and improve the efficiency of hydrate-based secondary refrigeration process. For that purpose, in the present work the real-time evolution of CO 2 concentration in the liquid phase was measured in situ during hydrate formation. CO 2 hydrates were formed within a stirred reactor equipped with an Attenuated Total Reflection probe coupled with a Fourier Transform Infra-Red spectroscopy analyzer. By comparing the measured concentration to calculations based on the assumptions of (a) a liquid-vapor equilibrium (LVE) and (b) a hydrate-liquid equilibrium (HLE), it was deduced that the crystallization kinetic is limited by CO 2 transfers from the vapor phase to the liquid phase, whatever the experimental conditions tested. As soon as hydrates start forming, the CO 2 concentration in the liquid phase almost instantaneously reaches the hydrate-vapor equilibrium (HVE) value at the experimental temperature, while the reactor pressure slowly decreases towards the LVE value defined by Henry’s law. Different stirring speeds were experimented in order to check the effect of enhancing CO 2 dissolution during hydrate formation. This resulted in faster dissolution of CO 2 , though still transfer-limited formation kinetics. [ABSTRACT FROM AUTHOR]

• Increasing precipitation is the main reason of land wetting. • Land drying is initially associated with precipitation deficit, and then increasing VPD amplifies the drying. • The estimated VPD contribution in the drying region is nearly 6 times of that of precipitation under high forcing pathways. • Elevated CO 2 concentration partly mitigates land drying by altering vegetation physiology. Increase Vapor Pressure Deficit (VPD) imposes higher atmospheric demand on land evaporation in the warming climate. However, it remains uncertain that how the increasing evaporative stress may enhance the global pattern of land drying. Here, we have used self-calibrating Palmer Drought Severity Index (scPDSI) based on outputs from 20 CMIP6 models to study the contribution of VPD, precipitation and other climatic factors to scPDSI changes globally. Global land drying and wetting are found to be regionally dependent, with statistically significant enhancement of drying and wetting under SSP2-4.5, SSP3-7.0 and SSP5-8.5 pathways (2015–2100) compared to the historical period (1961–2014). Increasing precipitation is the main reason of land wetting, while the land drying is initially associated with precipitation deficit, it is partly dominated by the increasing VPD over 20 ∼ 27% of the global land, where the estimated VPD contribution is nearly 6 times of that of precipitation under high forcing pathways. Elevated CO 2 concentration is suggested to partly mitigate land drying by altering vegetation physiology; however, this mitigation is quantified to be limited. Our findings highlight the key role of VPD in accelerating global pattern of land drying and its increasing dominance in the warming climate. [ABSTRACT FROM AUTHOR]

Abstract EnerPHit and low energy retrofitting projects are increasing in adoption to tackle greenhouse gas emissions target in the United Kingdom. While good energy reductions can be achieved, there is a growing concerned of overheating in these low energy projects with high levels of insulation and airtightness. The aim of this study was to evaluate the thermal comfort and Indoor Air Quality (IAQ) of a low energy dwelling in London based on EnerPHit principles to reduce energy consumption. This project concerns an 1860’s Victorian terrace house situated within a conservation area in Kentish Town North London. The design approach was to radically reduce its heating demand while using ecological materials that are moisture open. It was also important to hold onto the original features inside and out that define this house’s character. The approach chosen to monitor IAQ and thermal comfort was based on monitoring the following indoor hygrothermal conditions: internal air temperature, relative humidity (RH) and CO 2 concentration. Sensors were placed in every room of the dwelling for temperature and relative humidity. CO 2 concentration was measured in the lounge and bedroom 2. Low energy retrofits can be achieved in conservation areas but more importantly, indoor temperatures in the property can be maintain steadily between 19–20 degrees centigrade, while relative humidity will be comfortably in between the range of 40 % and 70 %, with CO 2 concentration levels well below the 1000 ppm readings as required for good air exchange and healthy IAQ. [ABSTRACT FROM AUTHOR]

Building ventilation systems are equipped to improve indoor air quality (IAQ) through bringing in the non-polluted outdoor air for occupants. Carbon dioxide (CO2) concertation level serves as one of the most critical indicators for IAQ and occupancy to control ventilation systems. Many control strategies (such as ASHRAE standard 62.1) utilize CO2 concertation to determine the necessarily supplied air amount in building space. However, many studies suggest that due to the CO2’s mixed dual functions in indicating IAQ and occupancy, a large discrepancy is observed between the CO2 estimated occupancy and actual occupancy, especially in space with multiple zones. These estimation errors not only result in inefficient control response but also wasted fan power in unoccupied space. To solve those problems, this study utilized indoor positioning system (IPS) to detect occupancy and select the critical zones. The proposed control strategy calibrates the outdoor air flow based on detected zone occupancy. To validate the proposed strategy, this study compared the outcomes with conventional pure CO2 based control strategy. The simulation results suggest the proposed method could achieve acceptable CO2 concentration under 1000ppm for most zones and over 25% energy saving from primary fans and cooling coil during a sample weekday and a sample weekend day. [ABSTRACT FROM AUTHOR]

The carbonation behavior of concrete with different blast furnace slag replacement ratios (0 %, 50 % and 70 %) at different CO 2 concentrations (natural carbonation at 0.04 % and accelerated carbonation at 1 % and 2 %) was investigated in terms of carbonation rate, carbonation products assemblage and pore structure. The results show that the porosity of concrete decreases with the increase in CO 2 concentration regardless of mix proportion. The lower porosity at a higher CO 2 concentration can lead to an underestimation of the natural carbonation coefficient from accelerated carbonation tests. The carbonation degree of the C-S-H is one of the key factors that determine the carbonation behavior at different CO 2 concentrations. A higher CO 2 concentration enhances the consumption of the high-density C-S-H and therefore the carbonation of unreacted clinker. However, the C-S-H formed from GGBFS hydration is carbonated to a more advanced state (considerable silica gel is formed) under natural carbonation. • Densification by carbonation can cause underestimation of natural carbonation rate. • CO 2 concentration influences the carbonation degree of hydration products differently. • Carbonation degree of C-S-H is more uneven under natural carbonation. • Accelerated carbonation at a higher CO 2 concentration densifies the pore structure. [ABSTRACT FROM AUTHOR]

Agricultural irrigation water is essential for global food production. Climate change may significantly increase future atmosphere evaporative demand, which can further intensify local water stress, particularly in arid and semi-arid regions. In this study, we investigate climate change impacts on future irrigation water use (IWU) change, with a focus on a semi-arid (Zhangye) region in Northwest China. Specifically, this approach estimates crop water demand using Penman-Monteith-[CO 2 ] equation which is modified to account for atmospheric CO 2 concentration impacts. The IWU is then calculated as the difference between crop water demand and effective precipitation. This approach is validated using observed IWU. Combined with climate projections from eight Earth System Models (ESMs), future (up to 2100) IWU changes under different CO 2 emission scenarios are evaluated. Results demonstrate that our Penman-Monteith-[CO 2 ] approach is robust in IWU estimation, with a relative error of 2.4% during the validation period of 2015–2020. In the medium emission scenario (SSP245), IWU has a significant increasing trend of 1.4 × 105 m3/yr during 2021–2100, which is mainly attributed to the increased future atmospheric evaporation demand. Interestingly, IWU presents a decreasing trend of − 1.3 × 105 m3/yr for the high emission scenario (SSP585). This is because strongly elevated CO 2 concentration levels can substantially increase crop water use efficiency – leading to reduced IWU, and this impact outweighs the increased atmospheric evaporation demand in the SSP585 scenario. Therefore, our study suggests that future IWU change is determined by both climate change and crop responses to atmospheric CO 2 concentration. Finally, we highlight that adjusting crop patterns can reduce both the IWU mean and variation changes, which can potentially alleviate local water stress. • We investigate irrigation change under elevated atmospheric CO 2 concentration ([CO 2 ]). • A physically based approach based on the modified Penman-Monteith equation is used. • Our approach is validated using multi-year observed irrigation data. • Crop water use efficiency responses to [CO 2 ] determine future irrigation water demand. • Adjusting crop types can significantly reduce future irrigation water use. [ABSTRACT FROM AUTHOR]

Global agricultural production has been significantly affected by climate change. As a large but also weak agricultural country, China must take corresponding adaptation measures in regard to climate change. As C3 and C4 crops have different carbon sequestration pathways, the responses of their growth to climate change are different. This study comprehensively compared the impacts of climate change on the growth of C3 and C4 crops in China by considering several key variables, such as solar radiation, temperature, precipitation, CO 2 concentration, and agro–climatic constraints. The WOFOST (WOrld FOod STudies) model was used to quantitatively simulate and analyze the impacts of these variables on crop yield under four different scenarios. The results show that 1) during the growth period, solar radiation had the most significant change, followed by temperature difference between day and night, daily minimum temperature, daily maximum temperature, and precipitation; 2) the growth indicators of both C3 and C4 crops were more strongly correlated with solar radiation and temperature; and 3) under the four scenarios, changes in temperature and solar radiation had negative effects on both C3 and C4 crops in most regions, and changes in CO 2 concentration had greater impacts on crop yields than other factors. This study revealed the temporal and spatial patterns of crop growth indicators under different climate change scenarios in the past 30 years, which provides a scientific basis for exploring how to adapt to climate change and provide higher levels of crop productivity in China. • Climate change impacts on the growth of the C3 and C4 crops were compared. • WOFOST model was used to analyze such impacts under four different scenarios. • Changes in solar radiation and temperature had negative effects on the C3 and C4 crops. • Changes in CO 2 concentration had greater impacts on crop yields than other factors. [ABSTRACT FROM AUTHOR]

The air change rate per hour (ACH) inside a dwelling depends on its envelope air-tightness, ventilation devices and weather conditions. However, the occupant behaviour of residential buildings in mild climates is a key factor for the resulting ACH, influencing the indoor air quality and thermal comfort. This study was based in a one-year measurement campaign aiming at the assessment of the influence of occupants on the ventilation conditions of a dwelling located in Porto, Portugal. The master bedroom was monitored using temperature, relative humidity and CO2 sensors and air-tightness was evaluated with blower-door tests. In addition, surveys were also carried out where the occupants registered these actions and their occupation in the studied room. In this study, it was found that the main actions performed by occupants with influence in the ACH were related with windows handling and air grill extraction vents regulation. The measurements allowed to define behavioural typical patterns. The results include the typical CO2 concentration profiles in the main room and its variation in function of occupant behaviour. It was found that opening the air grill extraction vents could vary the total ACH up to 92%. Opening windows at night could increase the total ACH up to 435%. Before the morning window opening the minimum ACH obtained was 0.37h-1 and the action of morning window opening lead to an average ACH around 4 h-1. [ABSTRACT FROM AUTHOR]

The response of vegetation to elevated atmospheric carbon dioxide (e CO 2 ) has opposing effects on terrestrial water fluxes, especially evapotranspiration. In particular, CO 2 fertilization may enhance plant growth, therefore increasing canopy transpiration, while a partial stomatal closure decreases leaf transpiration. In this study, the effects of e CO 2 on water fluxes at a managed montane grassland were monitored using two high precision weighable lysimeters exposed to ambient and elevated (+300 ppm relative to ambient conditions) CO 2 concentrations. During the growing season, e CO 2 led to a general decrease in evapotranspiration and an increase in seepage. It was shown that e CO 2 influences evapotranspiration primarily through the change in stomatal resistance, as no effect of e CO 2 on the leaf area index was confirmed. A CO 2 -dependent Penman–Monteith equation and actual evapotranspiration data from the lysimeters made it possible to estimate the effect of e CO 2 on stomatal resistance. e CO 2 was found to increase stomatal resistance by 50% relative to ambient conditions. A HYDRUS-1D model allowed a temporal extension of the experimental findings to the period of 1990–2021 and revealed high variability in the relative change in annual seepage under e CO 2 . The modeling exercise demonstrated that the effect of e CO 2 can be easily implemented in the Penman–Monteith equation, and if neglected, leads to overestimation of transpiration and underestimation of seepage, especially in the first post-drought seepage events. Our findings show that e CO 2 positively affects the water balance in montane grasslands, thus e CO 2 might be an important factor in mitigating the effects of warming and droughts in the future. We propose that the vegetation response to e CO 2 , in particular the effect on stomatal resistance, should be taken into account when assessing the effects of climate change on grassland water fluxes. This may also have large implications when studying the impact of climate change at a watershed scale. • Elevated CO 2 (e CO 2 ) reduced ET, increased stomatal resistance and increased seepage. • Effects of e CO 2 on ET were modeled using a CO 2 -dependent Penman–Monteith equation. • Soil water fluxes under e CO 2 were successfully modeled using a HYDRUS-1D model. • Neglecting the e CO 2 effect led to an overestimation of ET and an underestimation of seepage. [ABSTRACT FROM AUTHOR]

• The Barman model well captured the seasonal variations of nutrients (N, P, and Si) and CO 2 concentrations in reservoirs of the Seine Basin. • The processes regulating carbon and nutrient variations in these reservoirs were quantified by the model. • Trophic state and mean water depth of reservoir affect NO 3 − and DSi retention efficiency. Reservoirs are active reactors for the biogeochemical cycling of carbon (C) and nutrients (nitrogen: N, phosphorus: P, and silica: Si), however, our in-depth understanding of C and nutrient cycling in reservoirs is still limited by the fact that it involves a variety of closely linked and coupled biogeochemical and hydrological processes. In this study, the updated process-based Barman model was applied to three reservoirs of the Seine Basin during 2019–2020, considering the variations of carbon dioxide (CO 2) concentrations and key water quality variables. The model simulations captured well the observed seasonal variations of water quality variables, although discrepancies remained for some variables. According to the model, we found that: (1) the three reservoirs are autotrophic ecosystems and showed high removal efficiency of dissolved inorganic carbon and nutrients during 2019-2020; (2) phytoplankton assimilation, benthic denitrification, precipitation and dissolution of calcium carbonate, and gas exchange at the water-air interface are the dominant processes for water quality variations in reservoirs; (3) based on scenarios results, trophic state and mean water depth of reservoir would impact the biogeochemical processes and the retention efficiency of nitrate and dissolved silicate. Finally, we expect that the successful application of Barman model in the reservoirs of the Seine Basin could provide a useful tool for simulating reservoir water quality changes and thus evaluating the impacts of reservoirs on downstream water quality. [ABSTRACT FROM AUTHOR]

Studies have demonstrated that basic oxygen furnace slag (BOFS) powder can be granulated to produce a strong artificial aggregate through strengthening with accelerated carbonation. However, our previous results showed that a 100% CO 2 concentration applied during granulation could significantly degrade the properties of the produced BOFS aggregate due to the loss of bridging water upon undergoing a rapid exothermic reaction. Therefore, this paper aims to optimize the CO 2 concentration during granulation of BOFS and investigate the impact on the subsequent post air or CO 2 curing of the produced aggregates. According to X-ray computed tomography results, the CO 2 applied during granulation should be controlled at 40 vol% or less in order to provide proper connective pores in freshly granulated BOFS aggregates for subsequent carbonation, thereby allowing higher CO 2 uptake and better mechanical development of hardened BOFS aggregates. It was also noted that with a high granulation-CO 2 concentration typically of 100% can result in the formation of multiple granules in a single produced BOFS aggregate, hence lowering the intrinsic structure and aggregate strength. Compared to the CO 2 reaction that occurs during granulation, post CO 2 curing plays the main role in developing the mechanical strength of hardened BOFS aggregates. [Display omitted] • Optimization of CO 2 concentration during granulation of BOFS was studied. • Synchronized carbonation-granulation can control connective pores for carbonation. • High granulation-CO 2 concentration formed multiple granules in a single aggregate. • Post CO 2 curing played an important key to contribute the final strength. • It is economically feasible to produce high strength lightweight BOFS aggregate. [ABSTRACT FROM AUTHOR]

Direct absorption spectroscopy measurement of the 4. 3 μ m CO 2 using interband cascade laser with a high spectral resolution, provides theoretical feasibility to retrieve the spatial distribution of CO 2 temperature and concentration in flames. However, retrieving temperature and concentrations from the line-of-sight spectral measurements involves solving non-linear and ill-posed problems. Traditional reconstruction algorithms for axisymmetric flames require multiple line-of-sight measurements in both axial and radial directions. The complicated experimental system limits the reconstruction efficiency. Here, a novel reconstruction model is proposed and demonstrated based on the U-Net model, a fully convolutional network model composed by a encoder–decoder path forming a symmetric U-shaped architecture, which only requires measurements of the central axis of the flame to simultaneously and efficiently reconstruct the two-dimensional temperature and CO 2 concentration fields for axisymmetric flames. The U-Net model is trained using datasets from simulated temperature, CO 2 concentration and their corresponding spectral optical thickness. The proposed U-Net model has been applied to reconstruct the two-dimensional temperature and CO 2 concentration fields of two previously measured laminar diffusion flames. Comparing with results from the traditional Abel inversion and two-line atomic fluorescence thermometry methods, the U-Net reconstruction model can better preserve the spatial continuity and correlation of flame temperature and CO 2 concentration from information hidden in the flame spectral images, which considerably simplifies the measurement system and improves the reconstruction performance. • A U-Net model was proposed to reconstruct the 2-D flames scalar fields. • The proposed method requires fewer measurements only along the flame center. • The model preserves the spatial continuity better. • Results have shown good feasibility and high efficiency of the method. [ABSTRACT FROM AUTHOR]

• The influence mechanism of CO 2 , RH and temperature on cement-based materials was analyzed in detail. • The theoretical relationship between environmental factors and carbonation was analyzed. • The numerical analysis process of coupling effect of environmental factors on carbonation is introduced. • Based on the review of carbonation under different environmental factors, the future research directions are prospected. For in situ reinforced concrete structures, carbonation has been considered as a risk that needs to be inhibited for the past decades; while a pronounced carbonation in early age concretes is now regarded as a good method to reduce carbon footprint for civil engineering industry, and needs to be promoted. Therefore, a thorough understanding on controlling the extent of carbonation in various types of concretes and at different stages needs to be delivered, so as to meet the opposite demands in various cases. By controlling environmental conditions, including temperature, humidity and CO 2 concentration, different degrees of carbonation can be achieved. However, even though significant amount of carbonation works have been carried out, there is still a lack of a unified conclusion and summary discussion on the impacts from external factors. In this review, impacts of temperature, humidity, CO 2 concentration and their coupling effects on carbonation of concretes are summarised, aiming to facilitate promotion and inhibition of the process in practice. Meanwhile, future perspectives to gap the current research status and precise carbonation control are raised. [ABSTRACT FROM AUTHOR]

Worship places represent a unique type of buildings due to their functionality, dense occupancy, intermittent use, roof geometry, large inner space, and consumed energy of cooling/heating systems. In addition, thermal comfort and indoor air quality are decisive keys that affect the psychological and physiological conditions of occupants as well as their activity level and working efficiency. Though, a scarce number of studies focused on investigating the indoor conditions of worship places. Thus, a mosque located in Bahrain was selected to examine the influence of the occupancy level and period on thermal comfort sensation and indoor air quality. The readings of air temperature, humidity, air velocity, and CO 2 concentration were recorded during real several occupancy levels and periods during the summer season. The measured findings of PMV and PPD metrics indicated that the social distancing between worshippers, during the SARS-CoV-2 pandemic, causes a feeling of coolness under the existing cooling system. Meanwhile, the 2-h occupancy period produced a 75% increment of CO 2 concentration, 55% during 1-h occupancy, and 20% during half an hour occupancy. Therefore, the air-conditioning systems of worship places should be reconsidered in terms of ventilation rates and partial operating to provide comfortable conditions that accommodate different occupancy levels and periods. [ABSTRACT FROM AUTHOR]

In this study, we performed a comprehensive assessment of the vertical CO 2 concentration in the urban atmosphere using measurements at two different heights (113 m and 420 m) in Seoul, South Korea. The difference in CO 2 concentration between the two altitudes (△CO 2 = CO 2 at 113 m minus CO 2 at 420 m) showed a significant diurnal variation, with the highest at 07:00 (19.9 ppm) and the lowest at 16:00 (3.9 ppm). When the planetary boundary layer (PBL) rose above the two sites (daytime), the CO 2 concentrations at the two altitudes were highly correlated (r = 0.87) with low △CO 2. In contrast, when the PBL was located between the two sites (night time), the correlation coefficient of the CO 2 concentration between the two altitudes decreased by 0.55 with a high △CO 2. To explain the cause of this variation in △CO 2 according to PBL, we performed Weather Research and Forecasting-stochastic time-inverted Lagrangian transport (WRF-STILT) simulations. Simulations showed that CO 2 measurements at two different heights were influenced by the same nearby urban areas during the daytime. However, the site above the PBL only measured the CO 2 of air transported from the outside downtown area during the night time. Consequently, the observed night time △CO 2 is explained by the difference in air mass between the two measurements owing to PBL variations. The night time △CO 2 further implicates the local attribution of observed CO 2 below the PBL by removing the effect from the remote area. Because of this unique night time characteristic of △CO 2 , we evaluated the changes in CO 2 concentration in Seoul during the COVID-19 period. Compared to the pre-COVID-19 period, △CO 2 clearly decreased from 26.5 ppm to 6.2 ppm with the implementation of social distancing, thus confirming the decreasing local influence of CO 2 concentrations. Our findings highlight the potential of atmospheric CO 2 monitoring at high altitudes as an observation-based method to assess the effectiveness of local carbon management. • Emerging importance of tall tower CO 2 observation in carbon monitoring. • Observational evidence that PBL constrains the vertical variations of CO 2. • Urban atmospheric vertical structure can be identified via vertical CO 2 monitoring. • Variation of urban CO 2 emissions can be detected via vertical CO 2 monitoring. [ABSTRACT FROM AUTHOR]

• The combination of limestone-based dual-loop WFGD and oxygen-enriched combustion was proposed. • Main influence factors and reaction mechanism were fully investigated. • Effect of CO 2 concentration on desulfurization process of single-loop and dual-loop WFGD was compared. • Dual-loop WFGD has better adaptability to flue gas desulfurization after oxygen-enriched combustion. Oxygen-enriched combustion is the most promising CO 2 emission reduction technology for coal burning. However, the sharp increase in CO 2 and SO 2 concentrations in flue gas after oxygen-enriched combustion poses a new challenge to the subsequent wet flue gas desulfurization (WFGD) system. In this study, limestone-based dual-loop WFGD technology was used to solve this problem. Using a small dual-loop falling-film WFGD experimental system, the effect of CO 2 concentration on limestone dissolution, SO 2 absorption, SIV oxidation, and CaSO 4 crystallization during limestone-based dual-loop WFGD was investigated in detail and compared with single-loop WFGD. The results show that, although an increase in CO 2 concentration is beneficial to SO 2 absorption in the single-loop WFGD system, it is not conducive to limestone dissolution, SIV oxidation, and CaSO 4 crystallization. Compared with single-loop WFGD, in the low pH region of dual-loop WFGD, increasing the CO 2 concentration can also improve the SO 2 absorption efficiency. However, it had no obvious effect on limestone dissolution, SIV oxidation, and CaSO 4 crystallization. In the high pH region of the dual-loop WFGD, although an increase in CO 2 concentration is not conducive to SO 2 absorption, the SO 2 absorption efficiency is still higher than that of single-loop WFGD. The negative effect of increasing the CO 2 concentration on limestone dissolution, SIV oxidation, and CaSO 4 crystallization can be effectively solved by introducing slurry from the high pH region into the low pH region. Therefore, compared with single-loop WFGD technology, dual-loop WFGD is more suitable for flue gas desulfurization after oxygen-enriched combustion. [ABSTRACT FROM AUTHOR]

Ocean ventilation change in the subarctic Pacific Ocean is critical for regulating nutrients, heating, and ocean–atmosphere CO 2 exchange. Debate continues over whether direct ventilation in the subarctic Pacific Ocean has reached the deep/bottom oceans on different time scales over the last millions of years. Here, we studied the main and trace elements, including Si, Ca, Ba, Zn, Zr, and Rb, and stable nitrogen isotope signals between 5.5 and 2.5 Ma at Ocean Drilling Program (ODP) Site 882. Our results revealed that weakening of deep/bottom water circulation after 3.5 Ma at ODP Site 882 was strongly linked to slowdown of deep/bottom water ventilation in the Atlantic and Southern Ocean. Element results indicated increase in oxygen content between ~3.5 and 2.73 Ma, supporting the suggestion of North Pacific Deep Water formation. Surface vertical mixing strength varied over a long cycle of ~400 kyr during the Early- to Mid-Pliocene in the northwest subarctic Pacific Ocean, which was linked to sea surface temperature gradient between low- and high- latitude regions caused by solar radiation differences regulated by changes in the Earth's orbital eccentricity. • Deep ocean circulation weakened after 3.5 Ma in the subarctic Pacific Ocean. • The North Pacific Deep/Intermediate Water enhanced during 3.5–2.73 Ma. • The surface vertical mixing changed in a ~ 400 kyr cycle regulated by Earth's orbital eccentricity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Storm intensification was incorporated into the downscaling process of GCMs. • Amounts of runoff and soil loss from extreme storm events were assessed. • Crop rotation and no-till would effectively mitigate soil erosion under climate change. • Uncertainty of simulated runoff and soil loss was apportioned. Proper simulation of storm intensification is critical in projecting crop yield, surface runoff, and soil loss under climate change conditions. We developed a total of 100 climate scenarios coupled with storm intensification, which were based on 25 downscaled GCMs (General Circulation Model) projections under RCP4.5 and RCP8.5 (Representative Concentration Pathways) for two time periods of 2021–2050 and 2051–2080. The climate files were applied to a modified WEPP (Water Erosion Prediction Project) model to estimate crop yield, runoff, and soil loss under 29 combinations of cropping and tillage systems. The results showed that future extreme storm events in the study area would significantly increase during 2021–2080 (P < 0.01). However, average monthly precipitation in summer would decrease by 12.5% in June and 10.8% in July, along with an annual precipitation decline of 2.6%, leading to a decrease in crop yield in this rainfed agricultural region. The amount of runoff (soil loss) from extreme storms would account for 45.9 (64.3%) of the total annual runoff (soil loss) when averaged across two time periods and two RCPs. The average annual runoff depth (soil loss amount) from crop rotation or double cropping systems would be 27.6 (78.1%) less than the corresponding values in a continuous monoculture cropping system. No-till and crop rotations with alfalfa are the best agricultural management alternatives to mitigate soil erosion rates under future climate change. The analysis of variance (ANOVA) indicated that the uncertainty contributions of GCMs and cropping and tillage systems reached 45.5% and 30.4% in annual surface runoff prediction (P < 0.001), while cropping and tillage systems (71.7%, P < 0.001) was the major uncertainty source in annual soil loss simulations. This study improved the prediction of crop yield, runoff, and soil loss from various cropping and tillage systems under climate change conditions by integrating storm intensification from multiple GCM ensembles. [ABSTRACT FROM AUTHOR]

During COVID-19 lockdowns less people were able to fulfill the WHO recommendations on physical activity. Also, fitness centers were associated to SARS-CoV-2 superspreader events. However, the risk of infection can be strongly reduced by outdoor air ventilation. To investigate whether a reopening of fitness centers can be justified, CO 2 concentration was measured during four days in a fitness center. Except for one room, the observed CO 2 concentrations were mainly under 800 ppm, which stands for high air quality. The strong decrease of CO 2 concentration during the 15 min evacuations following each hour of workout, speaks for the functionality of the ventilation system. In particular, the number of people present in the studio has a strong impact on the estimated CO 2 value. In a linear mixed model, an additional CO 2 concentration of 2.24 ppm (95 % confidence interval [2.04, 2.43]) was estimated for this setting with a total volume of 4065 m 3 in the fitness center and a possible air change rate per hour up to 10. This means, that for 45 visitors, 100 ppm can be added to the predicted concentration. To summarize, a combination of ventilation, restriction of the number of visitors and surveying the CO 2 concentration allowing for further restrictions in case of need, seems to be an adequate means to reduce the risk of SARS-CoV-2 infection in fitness centers. • Real world data was observed measuring air quality in a fitness center with restrictions due to the COVID-19 pandemic with a special focus to air ventilation. • Except for one room, the CO 2 concentration was mainly under 800 ppm, which stands for high air quality. • During predefined breaks, the CO 2 concentration strongly decreased, showing the functionality of the ventilation system. • The number of visitors in the fitness center has a strong impact on the estimated CO 2 concentration. [ABSTRACT FROM AUTHOR]

Ventilation is of critical importance to containing COVID-19 contagion in indoor environments. Keeping the ventilation rate at high level is recommended by many guidelines to dilute virus-laden respiratory particles and mitigate airborne transmission risk. However, high ventilation rate will cause high energy use. Demand-controlled ventilation is a promising technology option for controlling indoor air quality in an energy-efficient manner. This paper proposes a novel CO 2 -based demand-controlled ventilation strategy to limit the spread of COVID-19 in indoor environments. First, the quantitative relationship is established between COVID-19 infection risk and average CO 2 level. Then, a sufficient condition is proposed to ensure COVID-19 event reproduction number is less than 1 under a conservative consideration of the number of infectors. Finally, a ventilation control scheme is designed to make sure the above condition can be satisfied. Case studies of different indoor environments have been conducted on a testbed of a real ventilation system to validate the effectiveness of the proposed strategy. Results show that the proposed strategy can efficiently maintain the reproduction number less than 1 to limit COVID-19 contagion while saving about 30%–50% of energy compared with the fixed ventilation scheme. The proposed strategy offers more practical values compared with existing studies: it is applicable to scenarios where there are multiple infectors, and the number of infectors varies with time; it only requires CO 2 sensors and does not require occupancy detection sensors. Since CO 2 sensors are very mature and low-cost, the proposed strategy is suitable for mass deployment in most existing ventilation systems. • A CO 2 -based DCV strategy is proposed to limit the spread of COVID-19. • Quantitative relationship is established between infection risk and CO 2 level. • A sufficient condition is proposed to ensure the reproduction number less than 1. • This strategy can achieve safe and energy-efficient control of infection risk. [ABSTRACT FROM AUTHOR]

The photoelectrochemical reduction of CO 2 provides a clean and sustainable route to produce value-added chemicals and fuels using sunlight as the energy source and greenhouse gas CO 2 as the feedstock. However, the use of pure CO 2 decreases the economic feasibility of the technology. Direct utilization of industrial flue gas is desirable for practical applications, but the effect of flue gas impurities and concentrations on the photoelectrochemical CO 2 reduction remains unknown. Herein, we investigate the influence of NO x , SO x and O 2 impurities and low CO 2 concentrations on photoelectrochemical CO 2 reduction performance using Au nanoparticles decorated GaN nanowire arrays on Si wafer as the model photoelectrode. It is found that the presence of NO x , SO x impurities, and low CO 2 concentrations are compatible with photoelectrochemical CO 2 reduction. In contrast, the inclusion of O 2 impurity reduces the CO 2 conversion efficiency. However, the effect of O 2 impurity is reversible and the photoelectrocatalytic activity is recovered once O 2 impurity is removed. The effects of flue gas impurities and concentrations on the photoelectrochemical CO 2 reduction performance were studied for the first time. [Display omitted] • The effects of flue gas impurities and concentrations on photoelectrochemical CO 2 reduction were investigated. • Au nanoparticles decorated GaN nanowire arrays on Si wafer was used as the platform photoelectrode. • The influences of NO x , SO x impurities, and low CO 2 concentrations were negligible. • O 2 impurity had a detrimental effect, but the effect was reversible. [ABSTRACT FROM AUTHOR]

• Demand-controlled ventilation for energy-efficient mechanical ventilation in pigsty. • Indoor temperature and CO 2 concentration prediction model was developed. • Changes in pig weights affected prediction performance. • 15-minute time step DCV control achieved smaller change in indoor temperature. The distribution of agricultural and livestock products has been limited owing to the recent rapid population growth and the COVID-19 pandemic; this has led to an increase in the demand for food security. The livestock industry is interested in increasing the growth performance of livestock that has resulted in the need for a mechanical ventilation system that can create a comfortable indoor environment. In this study, the applicability of demand-controlled ventilation (DCV) to energy-efficient mechanical ventilation control in a pigsty was analyzed. To this end, an indoor temperature and CO 2 concentration prediction model was developed, and the indoor environment and energy consumption behavior based on the application of DCV control were analyzed. As a result, when DCV control was applied, the energy consumption was smaller than that of the existing control method; however, when it was controlled in an hourly time step, the increase in indoor temperature was large, and several sections exceeded the maximum temperature. In addition, when it was controlled in 15-min time steps, the increase in indoor temperature and energy consumption decreased; however, it was not energy efficient on days with high-outdoor temperature and pig heat. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we systematically studied the effects of membrane thickness, CO2 concentration, and operating time on the CO2 flux density of an Al2O3-surface-modified and carbon-black-pore-former derived silver-carbonate membrane. It was found that the CO2 transport through a silver-carbonate membrane exhibited a critical thickness of 0.84mm, below which no flux enhancement could be achieved. The CO2 flux was also observed to be proportional to the difference of at the two reacting surfaces, and not the commonly assumed logarithmic partial pressure difference. The CO2 flux tested against time at 650°C increased by 200% for the first 160h, followed by a gradual decrease. At the 326-h marker, the flux was still the same as the original value when the test was started. Overall, the use of carbon black as a pore-former and Al2O3 as a surface modifier for silver-carbonate membranes has been proven effective and necessary to achieve a higher and more stable CO2 flux density. [Copyright &y& Elsevier]

Abstract: Carbonic anhydrases (CAs, EC 4.2.1.1) are metalloenzymes found throughout the phylogenetic tree. The β-class carbonic anhydrases (β-CAs) are the predominating class of CAs in plants. Growing evidence underscores the importance of β-CAs in plant immunity and environmental adaptation in addition to their roles in photosynthesis. However, many fundamental problems in Arabidopsis βCAs expression remain unsolved. Here we examined the transcript abundance of AtβCAs in different tissues of Arabidopsis thaliana, and the accumulation of mRNA in response to CO2 and darkness. Histochemical analysis was performed to study the promoter activity of AtβCAs during post-germination seedling growth and in mature plants. All six members of the AtβCA subfamily showed a response to changed CO2 level and darkness, but each member showed a specific dynamic pattern. Although expression of each AtβCA was unique, in general most AtβCAs were synchronously expressed in green leaves since 5 days after germination until flowering. AtβCA1 and AtβCA2 were most highly expressed in leaves but AtβCA2 displayed weaker expression in roots. The level of AtβCA3 transcripts was highest in flowers, while AtβCA5 was most widely expressed and might be involved in more processes than other members. AtβCA6 was unique for increased expression in darkness and no expression in either the anther or pistil. The present study provides useful information for further functional investigation. [Copyright &y& Elsevier]

Highlights: [•] Study the effects of temperature, pressure, dissolved CO2 and shear rate on the rheology of bitumen at the temperature range of −10°C to 180°C and pressures up to 15 MPa. [•] Model the flow properties of the bitumen–CO2 mixture by using the simple yet powerful reduced variable method. [•] Introduce the free volume concept modelling to account for the effect of dissolved CO2 on the viscosity of the bitumen–CO2 mixture more precisely. [•] Study the thixotropic behaviour of bitumen and bitumen–CO2 mixture. [ABSTRACT FROM AUTHOR]